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Results for “CITRIC ACID”

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PubMed1995

Modeling of liver citric acid cycle and gluconeogenesis based on 13C mass isotopomer distribution analysis of intermediates.

We have developed and implemented a model that can predict the positional isotopomer distribution of various hepatic metabolites labeled with [U-13C3]lactate and/or [U-13C3]pyruvate for given relative flux rates through the citric acid cycle and gluconeogenesis reactions. Our model includes (i) isotopic exchange between alpha-ketoglutarate and glutamate, (ii) a reversible isocitrate dehydrogenase reaction, (iii) an active ATP-citrate lyase, and (iv) aspartate and malate shuttles with separate cytosolic and mitochondrial pools for oxaloacetate, malate, and fumarate. A parameter estimation routine fit the mass isotopomer distribution of selected metabolites measured by gas chromatography-mass spectrometry to the model predicted distributions. We fit measured mass isotopomer distributions of phosphoenolpyruvate, citrate, alpha-ketoglutarate, glutamate, and pyruvate isolated from fasted rat livers perfused with [U-13C3]lactate + [U-13C3]pyruvate. This fitting yielded rates which we express relative to that of pyruvate carboxylase: citric acid cycle represented by the irreversible alpha-ketoglutarate dehydrogenase = 0.32; citrate synthase = 0.64; reversal of isocitrate dehydrogenase = 0.52; citrate lyase = 0.33, aspartate shuttle = 0.24, and malate shuttle = 0.44. Rates calculated for the cytosolic and mitochondrial fumarate and malate dehydrogenase reactions are subject to uncertainties as indicated by identifiability analyses. Previous forms of our model that did not include pyruvate kinase, exchange of alpha-ketoglutarate with glutamate, reversibility of isocitrate dehydrogenase, and/or ATP-citrate lyase activity were not as successful at predicting our measured values. This model offers a general tool for studying the regulation of the citric acid cycle and gluconeogenesis and can be readily modified for any 13C-labeled lactate or pyruvate substrate.

Animals↗

PubMed2003

The effect of irrigation with doxycycline or citric acid on leakage and osseous wound healing.

This study investigated the effect of doxycycline irrigation on wound healing and the apical seal of three filling materials. Part 1: 220 extracted teeth received root canal therapy followed by root resection (2 mm) and ultrasonic root end preparations (3 mm). Groups of 20 were irrigated with saline, citric acid, or doxycycline and filled with amalgam, Super EBA, or MTA. Leakage was measured (mm) after decalcification and clearing. Part 2: two defects were made on each side of the mandible of 10 New Zealand rabbits. On each side, one defect was irrigated with saline and one with either citric acid or doxycycline. The animals were killed in groups of five at 9 and 18 days. Sections of each defect were stained with hematoxylin and eosin for evaluation of healing and bone fill. Super EBA and MTA leaked significantly less than amalgam, regardless of irrigant. Leakage after irrigation with doxycycline compared to citric acid or saline was not significantly different for Super EBA or MTA but was lower for amalgam. There was no significant difference in healing or bone fill among irrigants at 9 or 18 days.

Aluminum Compounds↗

PubMed2003

A novel formulation of metal ions and citric acid reduces reactive oxygen species in vitro.

OBJECTIVE: Reactive oxygen species, including superoxide anions, are thought to play an important role in impairing wound healing. Additionally, superoxide anions react with nitric oxide produced by macrophages to form peroxynitrite, another strong oxidant with detrimental effects on surrounding tissue. This in vitro study investigated whether samples of metal ions and citric acid are able to reduce levels of reactive oxygen species. METHOD: Samples of materials were tested in assays for the following: inhibition of reactive oxygen species production by human polymorphonuclear neutrophils (PMNs); antioxidant activity (scavenging of superoxide anions in a cell-free system); inhibition of human complement (limiting the generation of complement factors that attract and stimulate PMNs, thereby reducing levels of reactive oxygen species). RESULTS: Metal ions were shown to inhibit both PMN production of reactive oxygen species and the activation of complement via the classical pathway, whereas citric acid was found to be a scavenger of superoxide anions. CONCLUSION: The beneficial effects of using formulations containing metal ions and citric acid on chronic wounds may be explained in part by a reduction of reactive oxygen species in these wounds.

Antioxidants↗

PubMed2003

Effect of phenolic compounds on the co-metabolism of citric acid and sugars by Oenococcus oeni from wine.

AIMS: The goal of this study was to examine the growth of Oenococcus oeni in the presence of phenolic compounds under wine conditions and to see how these compounds affect bacterial metabolism. METHODS AND RESULTS: Phenolic compounds have been added to a basal medium that simulates the composition of wine. Fifty milligrams per litre or more of phenolic compounds stimulated bacterial growth. Oenococcus oeni seemed to use citric acid and trehalose, if they were present, before glucose and fructose. Citrate was completely exhausted in three days and the yield of acetate was higher when phenolic compounds were present. CONCLUSIONS: Phenolic compounds reduced the rate of sugar consumption and enhanced citric acid consumption, increasing the yield of acetic acid. SIGNIFICANCE AND IMPACT OF THE STUDY: This study allows a better knowledge of co-metabolism of citric acid and sugars by O. oeni in the presence of phenolic compounds of wine.

Carbohydrate Metabolism↗

PubMed1995

Site specificity of citric acid retention after an oral rinse.

Erosion of the buccal incisor enamel, most frequent in the upper jaw, has been associated with excessive oral exposure to citric acid-containing foodstuffs. The aim of the study was to determine the retention of citric acid at different sites in the mouth after a standardized exposure. Thirty-four normal subjects rinsed with 95.2 mmol/l (2%) citric acid, pH 2.1, for 5 s. At 1 min 55 s after the rinse a preweighed cotton pellet was used to collect saliva samples from upper labial incisor surfaces (UB), lower labial incisor surfaces (LB) and sublingually (SL). The citric acid concentration was determined enzymatically. The concentrations were (mean +/- SD): 32.12 +/- 19.50, 11.90 +/- 8.60 and 1.52 +/- 1.90 mmol/l in the saliva collected from the UB, LB and SL sites, respectively. Analysis of variance revealed that the citric acid concentration in the upper incisor site differed significantly from that of the lower incisor site (p < 0.001) and the sublingual site (p < 0.001), and that the lower incisor site differed significantly from the sublingual site (p < 0.001). The individuals differed significantly with respect to citric acid retention (p < 0.05). A significant correlation was found between UB and LB sites (r = 0.61, p < 0.05).

Adult↗

PubMed2006

Na+-K+-2Cl- cotransporters and Cl- channels regulate citric acid cough in guinea pigs.

Loop diuretics have been shown to inhibit cough and other airway defensive reflexes via poorly defined mechanisms. We test the hypothesis that the furosemide-sensitive Na+-K+-2Cl- cotransporter (NKCC1) is expressed by sensory nerve fibers innervating the airways where it plays an important role in regulating sensory neural activity. NKCC1 immunoreactivity was present on the cell membranes of most nodose and jugular ganglia neurons projecting to the trachea, and it was present on the peripheral terminals of putative mechanosensory nerve fibers in the airways. In urethane-anesthetized, spontaneously breathing guinea pigs, bolus application of citric acid (1 mM to 2 M) to an isolated and perfused segment of the tracheal mucosa evoked coughing and respiratory slowing. Removal of Cl- from the tracheal perfusate evoked spontaneous coughing and significantly potentiated cough and respiratory slowing reflexes evoked by citric acid. The NKCC1 inhibitor furosemide (10-100 microM) significantly reduced both the number of coughs evoked by citric acid and the degree of acid-evoked respiratory slowing (P < 0.05). Localized tracheal pretreatment with the Cl- channel inhibitors DIDS or niflumic acid (100 microM) also significantly reduced cough, whereas the GABAA receptor agonist muscimol potentiated acid-evoked responses. These data suggest that vagal sensory neurons may accumulate Cl- due to the expression of the furosemide-sensitive Cl- transporter, NKCC1. Efflux of intracellular Cl-, in part through calcium-activated Cl- channels, may play an important role in regulating airway afferent neuron activity.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed1991

Periodontal healing following guided tissue regeneration with citric acid and fibronectin application.

This study was undertaken to determine the effects of guided tissue regeneration (GTR) with and without citric acid conditioning and autologous fibronectin application. The study subjects were four female beagle dogs with spontaneous periodontitis. The dogs were given thorough root debridement and 4 weeks later, mucoperiosteal flaps were raised on both sides of the mandible involving the 2nd, 3rd, and 4th premolar and 1st molar teeth. After debridement, notches were placed on the roots at the level of supporting bone. Citric acid (pH 1) was topically applied for 3 minutes on the exposed root surfaces of one side (experimental). The roots were irrigated with normal saline solution. Both the root surfaces and the inner surface of the flap were then bathed in autologous fibronectin in saline. Following this, Gore-Tex periodontal material was adapted to the roots of each tooth and sutured. The contralateral side, serving as control, was treated by surgery and application of Gore-Tex periodontal material only. All membranes were removed 1 month after surgery, and the dogs sacrificed at 3 months. Both mesio-distal and bucco-lingual microscopic histological sections were evaluated by descriptive histology, and linear measurements and surface area determination of the furcal tissues were made. Periodontal healing following the use of GTR procedure resulted in an increase in connective tissue and alveolar bone regeneration. Adjunctive critic acid plus autologous fibronectin produced slightly better results, but these differences were not statistically significant for this sample.

Acid Etching, Dental↗

PubMedDate not supplied

Effects of topical fluorides and citric acid on overglazed and autoglazed porcelain surfaces.

The effect of 1.23% acidulated phosphate fluoride, 0.40% stannous fluoride gels, and 2.00% citric acid solution on 150.00 overglazed and 150 autoglazed porcelain surfaces was measured using a profilometer. Application of 1.23% acidulated phosphate fluoride for periods of 16 and 32 minutes caused etching in both groups, but the autoglazed group was significantly more effected. In both groups increase in application time did not affect the amount of etching. No etching was detected in either group after the application of 0.40% stannous fluoride for 6 and 12 hours and 2.00% citric acid for 4 and 8 hours.

Acid Etching, Dental↗

PubMed1992

In vitro effects of citric acid application techniques on dentin surfaces.

The present study evaluated the in vitro effects of different application techniques of citric acid on dentin root surfaces. Ten freshly extracted, periodontally involved teeth were obtained and 4 dentin slabs, approximately 4 x 6 x 2 mm, were obtained from the roots of each tooth, for a total of 40 slabs. These slabs were identified by tooth and preserved in 1:1 anhydrous glycerol/absolute alcohol solution. Citric acid pH 1 was applied to 32 of the slabs for 5 minutes with one of 4 different techniques: 1) immersion; 2) placed with a saturated cotton pellet with no rubbing; 3) placed and burnished with a saturated cotton pellet; or 4) applied with a camel hair brush. The remaining 8 dentin slabs were used as negative control specimens, root-planed and non-acid treated. Following the various treatments, the slabs were fixed, dehydrated, critical point dried, and coated for scanning electron microscopic (SEM) evaluation. Scanning photomicrographs were obtained at 2,000, 6,000, and 40,000 magnifications. The surface characteristics of the treated dentin slabs were evaluated descriptively regarding the degree of fiber exposure; the number of exposed tubules and the surface area occupied by tubule orifices were also measured. Friedman's 2-way analysis for block designs was employed. Results demonstrated that root-planed, non-acid treated specimens had an amorphous, irregular surface which corresponded to a smear layer.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Topical↗

PubMed2006

Citric acid traps to replace sulphuric acid in the ammonia diffusion of dilute water samples for 15N analysis.

The analysis of 15N in aqueous samples requires the concentration of dissolved nitrogen (N) into a small volume that can be analysed by mass spectrometry. This is conveniently achieved by the NH3 diffusion technique, where NH4+ is captured on small acidified filters enclosed in PTFE. NO3- can be analysed the same way by reducing it to NH4+ with Devarda's alloy. H2SO4 is commonly used for the acidification of the filters. During combustion, however, this acid leads to the production of SO2 and elemental sulphur, which both have detrimental effects on the mass spectrometer. We propose here to replace H2SO4 with citric acid because it is combusted completely to CO2 and H2O in the elemental analyser before entering the mass spectrometer. Citric acid was found to give comparable results in terms of N recovery and 15N values, both for NH4+ and for NO3- samples. Blank samples revealed that N contamination was slightly lower using citric instead of sulphuric acid as acidifier of the glass filters. NH4+ samples first concentrated over cation-exchange columns were strongly acidic and several methods were tested to raise the pH for the subsequent diffusion. These samples gave incomplete N recoveries, but this problem was independent of the acid used on the filters and of the final pH of the sample. Complete recovery was achieved only by increasing the volume of the eluate from the columns. Citric acid can thus generally be recommended instead of H2SO4 for ammonia diffusion.

Journal Article↗

PubMed2005

Human enamel erosion in constant composition citric acid solutions as a function of degree of saturation with respect to hydroxyapatite.

The objective of this study was to investigate human enamel erosion under constant composition conditions, as a function of solution degree of saturation (DS) with respect to hydroxyapatite. The experimental conditions were relevant to the initial stages of enamel erosion by soft drinks. Nanoindentation was used to compare enamel surface softening caused by a control mineral water and two citric acid solutions with DS = 0.000 and DS = 0.032, both having pH 3.30. Enamel hardness and reduced elastic modulus were measured after 0, 30, 60, 120, 300 and 600 s exposure. A statistically significant change in enamel hardness was detected after 30 s exposure to both citric acid solutions, indicating that nanoindentation is extremely sensitive to the initial stages of erosion. There was a statistically significant difference between the mechanical properties of enamel exposed to the two citric acid solutions after 30, 60 and 120 s. At these times, the solution with DS = 0.000 caused twice as much enamel softening as that with DS = 0.032. This demonstrates that it may be possible to design a soft drink with a low erosive potential and a good taste by a small change in DS, at a typical drink pH.

Beverages↗

PubMed1976

The citric acid fermentation by Aspergillus niger: regulation by zinc of growth and acidogenesis.

The citric acid fermentation by Aspergillus niger is divided into two consecutive phases, a growth phase when the cells proliferate but do not accumulate citrate, followed by an accumulating phase when they produce citrate but do not proliferate, or else do so at a much reduced rate. When studied in a low sucrose (0.4-0.8%) mpinimal salts medium the growth-accumulation alternative was controlled by the concentration of zinc: high zinc (about 1-2 muM) maintained growth phase, while at low zinc (below 1 muM) growth became limited by zinc deficiency and the cultures passed into accumulating phase. Addition of zinc to accumulating cultures resulted in their reversion to growth phase. Iron, manganese, calcium at concentrations as high as 5-10 muM had no influence on either growth or citrate accumulation. These results suggest that zinc plays a role in the regulation of growth and citric acid accumulation.

Aspergillus↗

PubMed1978

Improved production of citric acid by a diploid strain of Aspergillus niger.

Aspergillus niger strain CGU 87 was treated with UV radiation and some auxotrophic mutants were obtained. These mutants were less productive than CGU 87, which produced an average of 7.4% citric acid. All possible crosses in pair wise combinations were carried out between these auxotrophs, and three heterokaryons were synthesised. Finally, one heterozygous diploid was isolated from each of them. These heterokaryons and diploids showed improved productivity when compared with their component parents, but except in one diploid D5, all others produced less citric acid than CGU 87. The yield of D5 exceeded that of CGU 87 by 1.2 times and it produced 9% citric acid. This is a significant improvement and the increased productivity seems to be the result of successful adaptation of D5 to its fermentation environment.

Aspergillus niger↗

PubMed1993

The effect of citric acid application on periodontally involved root surfaces. II. An in vitro scanning electron microscopic study.

The in vitro effect of citric acid application on periodontally involved root surfaces was investigated using scanning electron microscopy. Teeth were selected following specific criteria. The specimens were prepared for observation, and the features of the root surface were studied. The results demonstrated that a 3-minute application of citric acid (pH = 1.0) to the root surface after scaling and root planing demineralized the outer root surface, opened the dentinal tubules, and exposed collagen fibers. Scaling and root planing alone left the surface with a smear layer, scattered islands of cementum, and no collagen fibers or exposed dentinal tubules.

Citrates↗

PubMed1998

Use of citric acid for neutralizing polymerase chain reaction inhibition by chlorogenic acid in potato extracts.

Polyphenolics are a widely distributed class of plant constituents implicated in the inhibition of the polymerase chain reaction (PCR). Since chlorogenic acid forms the bulk of phenolics in the potato tuber, a range of chlorogenic acid concentrations were tested for inhibition of reverse transcription (RT) and PCR steps. The RT step was inhibited at chlorogenic acid concentrations of 6.0 to 7.5 microg, while the PCR step was inhibited at much lower concentrations of 1.2 to 1.8 microg. Incorporation of 1.2% citric acid at the nucleic acid extraction step prevented darkening of the extract and neutralized the inhibitory effect of chlorogenic acid.

Chlorogenic Acid↗

PubMed1995

Airway sensory replacement combined with nicotine replacement for smoking cessation. A randomized, placebo-controlled trial using a citric acid inhaler.

STUDY OBJECTIVE: This study was conducted to determine if the combination of airway sensory replacement and nicotine replacement improves 10-week smoking abstinence rates over nicotine replacement alone. DESIGN: Double-blind, randomized, placebo-controlled trial. SETTING: Outpatient research clinic. PARTICIPANTS: One hundred healthy volunteers who smoked at least one pack of cigarettes per day and desired to quit smoking. INTERVENTIONS: Subjects received either citric acid (n = 41) or lactose placebo (n = 59) inhalers to cope with smoking urges for 10 weeks. All subjects received self-help materials and nicotine patches for 6 weeks. Return visits were at weeks 1, 4, 6, and 10. Abstinence was defined as zero cigarettes smoked since the quit date verified by exhaled carbon monoxide < or = 8 ppm at all return visits. Inhaler effects were measured by a standardized questionnaire. MEASUREMENTS AND RESULTS: The primary outcome of continuous abstinence at the end of the 10-week treatment period was 19.5% (95% confidence interval [CI] = 7.4 to 31.6%) for the citric acid group vs 6.8% (95% CI = 0.4 to 13.2%) for the lactose group (p = 0.05). Relief from craving and short-term abstinence increased as airway sensations from the inhaler also increased. Abstinence at 10 weeks for subjects receiving strong airway sensations from the inhalers was 33.3% (95% CI = 14.5 to 52.1%). At 6 months, there was no difference in abstinence between the treatment groups (0% vs 5.1%, p = 0.20). CONCLUSIONS: When combined with the nicotine patch, the citric acid inhaler improved 10-week smoking abstinence over lactose inhaler. The combination of airway sensory replacement and nicotine replacement may prove beneficial for smoking cessation.

Administration, Cutaneous↗

PubMed2003

Copper-catalyzed oxidation of a structured lipid-based emulsion containing alpha-tocopherol and citric acid: influence of pH and NaCl.

The effects of salt and pH on copper-catalyzed lipid oxidation in structured lipid-based emulsions were evaluated. Ten percent oil-in-water emulsions were formulated with a canola oil/caprylic acid structured lipid and stabilized with 0.5% whey protein isolate. alpha-Tocopherol and citric acid were added to the emulsions to determine how changes in pH or the addition of NaCl affected their antioxidant activity. The peroxide values and anisidine values of emulsions stored at 50 degrees C were measured over an 8-day period. Increased lipid oxidation occurred in the pH 7.0 emulsions and when 0.5 M NaCl was added to the pH 3.0 samples. Adding alpha-tocopherol, citric acid, or a combination of the two compounds slowed the formation of hydroperoxides and their subsequent decomposition products in pH 3.0 emulsions.

Antioxidants↗

PubMedDate not supplied

Effect of time on the remineralisation of enamel by synthetic saliva after citric acid erosion.

The aim of this in vitro study was to determine the influence of remineralisation time on rehardening of surface-softened enamel after citric acid erosion. Seven groups of 13 samples of human enamel were eroded in 0.3% citric acid at pH 3.2 for 2 h followed by profilometric measurements. Individual groups of specimens were placed in artificial saliva for 1, 2, 4, 6, 9 or 24 h. A control group was placed in isotonic saline for 24 h. After new profilometric measurements samples were ultrasonicated stepwise up to 480 s with profilometric measurements performed at 5, 30, 120, 240 and 480 s to measure the depth of surface softening. The control group had a softened surface layer of mean thickness 2.9 microm. Mineral deposition was seen at all remineralisation times by scanning electron microscopy. Exposure to artificial saliva for 1, 2 or 4 h produced a partial rehardening of the softened enamel; the additional surface losses produced by ultrasonication were lower and time delayed compared to the control group. Specimens remineralised for 6, 9 and 24 h showed little evidence of surface loss after ultrasonication. The data suggest that a complete rehardening of the softened enamel in vitro is reached after a remineralisation time of 6 h. These data are of clinical relevance to tooth wear. However, there is a need for studies in situ of enamel demineralisation and remineralisation.

Analysis of Variance↗